/*
 *
 * (c) Copyright Ascensio System Limited 2010-2020
 *
 * This program is freeware. You can redistribute it and/or modify it under the terms of the GNU 
 * General Public License (GPL) version 3 as published by the Free Software Foundation (https://www.gnu.org/copyleft/gpl.html). 
 * In accordance with Section 7(a) of the GNU GPL its Section 15 shall be amended to the effect that 
 * Ascensio System SIA expressly excludes the warranty of non-infringement of any third-party rights.
 *
 * THIS PROGRAM IS DISTRIBUTED WITHOUT ANY WARRANTY; WITHOUT EVEN THE IMPLIED WARRANTY OF MERCHANTABILITY OR
 * FITNESS FOR A PARTICULAR PURPOSE. For more details, see GNU GPL at https://www.gnu.org/copyleft/gpl.html
 *
 * You can contact Ascensio System SIA by email at sales@onlyoffice.com
 *
 * The interactive user interfaces in modified source and object code versions of ONLYOFFICE must display 
 * Appropriate Legal Notices, as required under Section 5 of the GNU GPL version 3.
 *
 * Pursuant to Section 7 § 3(b) of the GNU GPL you must retain the original ONLYOFFICE logo which contains 
 * relevant author attributions when distributing the software. If the display of the logo in its graphic 
 * form is not reasonably feasible for technical reasons, you must include the words "Powered by ONLYOFFICE" 
 * in every copy of the program you distribute. 
 * Pursuant to Section 7 § 3(e) we decline to grant you any rights under trademark law for use of our trademarks.
 *
*/


/*
 * ShortURL (https://github.com/delight-im/ShortURL)
 * Copyright (c) delight.im (https://www.delight.im/)
 * Licensed under the MIT License (https://opensource.org/licenses/MIT)
 */

/**
 * ShortURL: Bijective conversion between natural numbers (IDs) and short strings
 *
 * ShortURL.encode() takes an ID and turns it into a short string
 * ShortURL.decode() takes a short string and turns it into an ID
 *
 * Features:
 * + large alphabet (51 chars) and thus very short resulting strings
 * + proof against offensive words (removed 'a', 'e', 'i', 'o' and 'u')
 * + unambiguous (removed 'I', 'l', '1', 'O' and '0')
 *
 * Example output:
 * 123456789 <=> pgK8p
 */

 //'23456789bcdfghjkmnpqrstvwxyzBCDFGHJKLMNPQRSTVWXYZ-_'

var _alphabet = "5XzpDt6wZRdsTrJkSY_cgPyxN4j-fnb9WKBF8vh3GH72QqmLVCM",
	_base = _alphabet.length,
	_initial = _base * _base;

module.exports = {

	encode: function(num) {
		num += _initial;
		var str = '';
		while (num > 0) {
			str = _alphabet.charAt(num % _base) + str;
			num = Math.floor(num / _base);
		}
		return str;
	},

	decode: function(str) {
		var num = 0;
		for (var i = 0; i < str.length; i++) {
            let index = _alphabet.indexOf(str.charAt(i));
            if (index < 0) return null;
			num = num * _base + index;
		}
		return num - _initial;
    }

};